Coming Soon? RoboDerby’s 3D printed robots.

[Brian..]

There's no stage more rewarding than making the first moving components. I know that you've had to deal with a couple of technical problems that would have left me scratching my head.  Great progress.

 

I like the rakish angle of the motor. 

[robothut]

I have too ask. about the 2 gears. I try to never add a gear in to the design unless I want to change the gear ratio. So what have you got in mind here ? Yes on my Roto-matic I did have a extra gear in the Geneva drive to align and change rotation. Can not wait to see how your first project turns out. Good work and have fun. Its not worth doing unless its fun also, well not to me any way. few things have been more fun that designing and 3d printing mechanical toys.

[RoboDerby]

1 hour ago, robothut said:

 

I have too ask. about the 2 gears.

 

 

7 hours ago, Brian.. said:

I like the rakish angle of the motor. 

Regarding the multiple gears, I want to have arm and head motion along with the walking. I tried to consider different linkages and mechanical actuators. But, I wasn’t having much success devising how to make it all work and fit in the design. The bottom gear will already have a pin on it that will run through a slot in the leg to drive the walking. I thought it might be tricky to add a link to drive the arms directly from the same gear. Even if I use linkage to drive the arms, I am unsure of how to then bring the motion over to the head, especially since the idea is to drive the head at half the speed of the arms and legs and I’m not clear on how to design a linkage to change the ratio. 
 

When it comes down to it, I think that I just better understand how gears work than I do different linkage designs. Thus when trying to imagine in my mind how to transfer motion and speed, I have an easier time thinking in terms of gearing. As I build up this design and actually see it in front of me, I might better be able to visualize refinements and possibly eliminate the extra gear. I am studying up the best I can on different mechanical systems and strategies. But, presently, my knowledge is still very limited and my brain is just working with what it currently understands. No doubt I will find more efficient and better ways to do things as I progress and gain more hands on experience.

 

As for the rake on the motor mount Brian, this was so that I could align the existing hole in the gear box that I am using for the shaft of the second gear more towards the center of the body and on more of a vertical axis to the driving gear. This was primarily to ensure that I didn’t run into space issues later on in the design.

 

For now, I am just experimenting and having fun. Nothing is concrete in the design so far.
 

[Roboto]

What a great beginning!!

[RoboDerby]

It’s coming along gang! I had to cut some material off the base plate of the motor mount that was preventing full range of motion. But this will be solved in a simple adjustment of my design in Fusion360. It is coming along though. Next I will work on the design for the wheel carriages and ratchet system that will be installed in the feet.
 

I should also mention that the final design will use the slower 1:120 geared motor. But I only have two of the slower speed variations, so I am doing the testing with the faster motor in case somehow it gets damaged in testing.
 

 

By the way, for John or Brian or any other printers in the group, has anyone ever tried PolyMaker PolyMax PLA? It doesn’t print well using the settings I have for my Paramount filament and I am unsure whether it is a temp issue or whether I should be looking at flow and retraction settings. Here is a photo of what the first prints looked like. Maybe there are some clues you recognize that might indicate a specific problem?

 The cam prints well enough. But you can see the teeth on the gear are a mess.

 

[Brian..]

Coming along nicely, Jeremy. Your leg design is an interesting one. By placing the motor cam slots in the lower part of the leg and the fulcrum above it you've achieved a very compact design. The next stage is the really interesting one, keeping those feet parallel with the ground and balancing everything  It took me a month of tinkering to understand what was going on. Your design means that you probably won't have a problem balancing the robot. It's the long-leggedy robots that have you pulling your hair out.  

 

The gear wheels do indicate that you need to alter the printer settings.  It looks like a retraction issue or too high a nozzle temperature but instead of tinkering I would download a printer profile for the Polymaker PLA and use it.  Don't get too fixated with retraction and flow settings if you can avoid it. I've never had to alter either. 

[RoboDerby]

Thanks Brian. As I already have access to the inside of a pug piston action robot for my mod project (which by God I’ll get back too eventually), I am using that as a reference for my design.

 

I have changed some dimensions here and there to accommodate the use of the dual axle motor. But I think the design will still work as long as I respect the relationships between the linkages. Basically when the front of the leg is 90 degrees to the ground, the linkages form a rectangle with  the axle of the cam gear centered and equidistant from the two upper connection points. In this configuration, as long as the axle stays equidistant horizontally between the two upper points, changing the vertical relationship will only change the length of the stride. In operation the linkage is just a scissoring parallelogram as far as I can tell. 
 

One flaw in my design from an engineering perspective is the angular stress put on the gear by having the cam positioned on its outer diameter. I’m not sure that it is a critical flaw. But I could remedy this to some degree either by using a larger diameter off center cam similar to what I have seen in some of John’s designs or by keeping the cam the same but rather than attaching it to the face of the gear, instead connecting it to an arm that attaches to the center of the gear and extends parallel to its face out to the cam position. But for now, I’m not sure it will be necessary to make such a change. 
 

Also, I had originally thought that I would move the arms via another gear above the driving gear. But by extending the cam further out through the leg, I might be able to drive the arm linkage with the cam as well. Though I think I will still add more gears to bring a 2:1 turning movement up to the head.

 

As for the filament, I think I will try running it at the lowest end of the suggested temperature range and go from there. I’ve tried searching for threads on PolyMax. But there is really very little information on people’s recommended settings, much less a profile designed for use with the filament. So far, I have had great results with Paramount 3D filaments making minor adjustments to Chep’s profiles. I found some fantastic settings from another person for easily removed supports as well. Personally I don’t like the idea of messing with retraction either if I don’t have to. 

 

 

[robothut]

One thing to keep in mind when printing gears with Cam pins in the position you printed in. If a 3d print is going to break it will always break on the layer lines, never the other direction. So there is a good chance the came pins if small in diameter will break off in shipping the way you have printed the part. There are several option's. One is to change to the larger diameter cam pin, or replace the cam pin with a hole in the gear that you can put in a metal cam pin shaft or screw. And there is always change the position of the gear and cam pin for printing, the down side to changing the position is you either have to use supports or you have to cut the part in too two parts and then glue together. You might take a look at the 3d printed Mexican robot I did, there should be threads here on he drome and I think its is thing-I-verse. Any way it has walking design like you are doing and drives the arm linkage.

[RoboDerby]

11 hours ago, robothut said:

One thing to keep in mind when printing gears with Cam pins in the position you printed in. If a 3d print is going to break it will always break on the layer lines, never the other direction. So there is a good chance the came pins if small in diameter will break off in shipping the way you have printed the part. There are several option's. One is to change to the larger diameter cam pin, or replace the cam pin with a hole in the gear that you can put in a metal cam pin shaft or screw. And there is always change the position of the gear and cam pin for printing, the down side to changing the position is you either have to use supports or you have to cut the part in too two parts and then glue together. You might take a look at the 3d printed Mexican robot I did, there should be threads here on he drome and I think its is thing-I-verse. Any way it has walking design like you are doing and drives the arm linkage.

I’ll have to check out your posts on the Mexican Robot. I consider myself lucky to have one of them on my shelf in fact thanks to Paul. But you are right about the cam. I had hoped printing it in PolyMax might negate the issue. But I tested it today attempting to bend it with a pair of pliers to see how much flex it would have and of course it snapped relatively easily. I think I may print the cam separately from the gear and create a hexagonal key way in the face of the gear for the cam to fit and secure from the back with a longer screw. I’m not sure there will be enough room to increase the size of the cam much  without interfering with the rear linkage of the wheel carriage. 
 

Also, after describing the linkage as a scissoring parallelogram in my previous comment, I realized that this is not an accurate assessment as with three fixed axiis this wouldn’t be possible. 

[Brian..]

Print it with a hole through, then glue in a pin. Quick and easy.   

 

 

[RoboDerby]

Thanks Brian. Great suggestion. Might save me from having to separate the cam from the gear for printing. Though if I go that route, I may use a screw from the back rather than a pin. 6 in the morning here and I’ve been up for hours trying to get the hang of the simulated motion function in Fusion360. In the end, I’m not sure that the joint motion link tool is set up to accommodate an offset cam on a gear like this. I was hoping to verify that the cam and rear rod that connects to the wheel carriage would not interfere with each other. Oh well. I think there is enough room to make the design work. I’ll just have to print the rear rod and see.

[Andyman]

And so, another mad Alphadrome scientist is born.

[robothut]

As slow as 3d printing parts is, it could still be faster than trying to get a simulation program to work right. And in the end no matter what the simulation program shows the only way to know if it works is too make it. So I say just do it and if it fails do it again.

[Morbius]

Fantastic work on this Roboderby!  

[nasa]

Way to go Jeremy.......you are off and running......congrats!